Bottom of a shaft furnace, a shaft furnace provided with such a bottom and a method for cooling such a bottom

ABSTRACT

A shaft furnace, e. g., blast furnace for iron manufacture, having liquid cooling of its periphery and air cooling of its bottom which contains a horizontal layer of refractory material with a heat conduction coefficient lambda (cal/m/h/*C) which under operating conditions is higher than 20, includes the improvement that said layer is enclosed between upper and lower layers of refractory of much lower heat conducting coefficient lambda . With the bottom surface cooled to below about 150* C, the thicknesses of said upper and lower layers, depending on their said coefficients, are preferably such that only 20 to 60 percent, more preferably 25 to 40 percent, of the heat discharge through the intermediate layer is transmitted to the lower layer; the periphery of the bottom being kept at about 50* C. The intermediate layer may consist of graphite with a lambda -value of 60 to 100; the lower, of refractory e. g., carbon bricks, of a lambda -vslue of 2 to 5; and the upper layer of refractory, e. g., semi-graphite, may have a lambda -value of 20 to 30. In particular embodiments the three layers, from top to bottom may have lambda -values of about 25, 80 and 4, and thicknesses about 60, 120 and 60 cm, and the upper layer may be shielded by a top layer, e. g., of magnesite of a thickness of about 35 cm.

United States Patent [1 1 Van Laar et al.

Aug. 14, 1973 BOTTOM OF A SHAFT FURNACE, A SHAFT FURNACE PROVIDED WITHSUCH A BOTTOM AND A METHOD FOR COOLING SUCH A BOTTOM [75] inventors:Jacobus Van Laar, Santpoort;

Bastiaan Martinus Hoogendoorn, l-ieemskerk, both of Netherlands; KarlWilhelm Friedrich Etzel, Frankfurt am Main, Germany [73] Assignee:Koninklyke Nederlandsche,

Hoogovens En, Netherlands [22] Filed: Dec. 17, 1971 [21] Appl. No.:209,089

[30] Foreign Application Priority Data Dec. 18, 1970 Netherlands 7018539[56] References Cited UNITED STATES PATENTS MacPherson et al. 263/44Snyder 266/32 Primary Examiner-John J. Camby Attorney-Hall & Houghton 7]ABSTRACT A shaft furnace, e. g., blast fumace for iron manufacture,having liquid cooling of its periphery and air cooling of its bottomwhich contains a horizontal layer of refractory material with aheatconduction coefficient A (cal/m/h/C) which under operating conditions ishigher than 20, includes the improvement that said layer is enclosedbetween upper and lower layers of re fractory of much lower heatconducting coefficient A. With the bottom surface cooled to below aboutl$0 C, the thicknesses of said upper and lower layers, depending ontheir said coefficients, are preferably such that only to 60 percent,more preferably to 40 percent, of the heat discharge through theintermediate layer is transmitted to the lower layer; the periphery ofthe bottom being kept at about C. The intermediate layer may consist ofgraphite with a A-value of to the lower, of refractory e. g., carbonbricks, of a )t-vslue of 2 to 5; and the upper layer of refractory, e.g., semi-graphite, may have a )t-value of 20 to 30.

of a thickness of about 35 cm.

15 Claims, 1 Drawing Figure BOTTOM OF A SHAFT FURNACE, A SHAFT FURNACEPROVIDED WITH SUCH A BOTTOM AND A METHOD FOR COOLING SUCH A BOTTOM Thisinvention first of all relates to a bottom of a shaft furnace, inparticular of a blast furnace for iron manufacture, of the type withliquid cooling along the periphery and air cooling along the lowersurface, in which this bottom contains a horizontal layer of refractorymaterial with a heat conduction coefficient A, which under operatingconditions is higher than 20 kcal/m/h/C. Moreover the invention relatesto a method for cooling such a bottom and to a shaft fr1rnace, providedwith such a bottom.

It is remarked that liquid cooling in this specification and in theclaims not only means spray cooling, but also evaporation cooling andcooling by convection.

The invention will be described in more detail below with particularreference to the application thereof to a blast furnace for ironproduction, but the invention could in corresponding manner be appliedto the bottoms of other shaft furnaces such as cupoIa-furnaces and'thelike. Y

In a blast furnace the bottom is subjected to a continuous heavy thermalload as a result of the quantity of liquid iron present immediately ontop of this bottom. The temperature in the zone of the tap hole is aboutl,400 to l,500 C. The bottom should be resistant against such hightemperatures, but moreover it has the function to support a considerablepart of the blast furnace structure and the contents thereof.

In order to meet the requirement of its supporting funtion it isnecessary that the bottom in those parts, which substantially supportthe structure, be sufficiently low in temperature.

A complication for blast furnace bottoms consists in that they aregradually attacked by the liquid iron. It may be said that for mostrefractory matrials used for the bottom this liquid iron has thetendency to penetrate into it to a depth where the temperature of thisbottom material about corresponds to the solidification temperature ofthe iron, which is l,l20 to 1,140 C. The zone above this temperaturelimit will gradually be attacked and deteriorated, so that the saidtemperature limit is displaced downwardly until a situation ofequilibrium has been reached.

In the space thus obtained, the so-called salamander, a temperaturegradient is found over the height thereof. This salamander is filledfrom above to its lower end with liquid iron and in part possibly withsolidified iron, and often also in part with a coke matrix.

It is of the utmost importance that in this situation of equilibirum thesalamander has the lowest possible height. This is so because a highsalamander means not only that there is much loss of material in thebottom of the furnace, but also has as a result that the temperature inthe foundation of the bottom becomes higher, which is an even much moreserious disadvantage. It is even possible that thereby the supportingfunction of this foundation is spoiled. Also for other reasons relatingto the production of pigiron it is undesirable that a high salamander isformed. Thus it has been aimed at in the past to embody the bottomstructures in such a way that the salamander remains as shallow aspossible and that the temperature in the foundation remains as low aspossible. A modern development consists in that the bottom is embodiedwith a relatively small thickness and that along the periphery it iscooled with the aid of liquid cooling and along the lower surface it iscooled with the aid of aircooling. In Journal of the Iron and SteelInstitute" of September 1967 such a structure has been described, whichfor the rest is for the greater part built up of carbon bricks. In thisstructure the bottom rests on a bottom plate or slab, which at its lowersurface is cooled by air circulation, there being a thin layer ofgraphite, having a thickness of about 30 cm, positioned upon this steelslab. This graphite layer has as its function to warrant a good thermalcontact between the refractory bottom material and the steel slab. Inthis structure a considerable part of the total heat flow will bedischarged through the lower surface of the bottom. An advantage of thissolution consists in that the bottom can be relatively thin and that itis possible to decrease the salamander additionally.

For very large furnaces this structure does, however, not give asatisfactory solution. It has appeared that in such large structuresthere is still the need to decrease the size of the salamanderadditionally, or the heat discharge through the lower surface of thebottom becomes so considerable that a cooling with air of this lowersurface is not sufficient. If it is nevertheless de' sired to restrict.the temperature of the bottom slab to about C,'it will be necessary toapply water cooling of the lower surface of the bottom. Such a solutionwill, however, entrain great risks as by a disturbance or a fall-out ofthis water cooling system of the lower surface of the bottom thetemperature will rapidly rise to undesired values, which givesconsiderable risk of collapse of the bottom. The said disadvantage of asalamander which is too deep could be removed by manufacturing theentire bottom from a material which is better heat-conductive, but inthis case the disadvantage will remain or the danger will even increasethat the operation of a furnace with such a bottom entrains great risks,particularly in case of fall-out of the water cooling of the lowersurface.

In view of the above the present invention aims at giving a structurewhich does not show the disadvantages of such known structures and whichnevertheless only forms a salamander of small dimensions and particularyof small height.

In view. thereof the invention is characterized in that the bottomcontains a horizontal layer of refractory material in a manner known assuch, with a heat conduction coefficient A under operating conditionsmeeting the requirement that it be higher than 20 kcal/m/h/C, and thatthis layer at: its upper and lower surface is enclosed by an upper layerand a lower layer of refractory material with a very much lower heatconduction coefficient A than the first said intermediary layer. Due tothis structure of the bottom it is possible to embody the cooling of thebottom according to the present invention in such a way that duringoperation the lower surface of the bottom is kept cooled to atemperature below about C in a manner known as such, preferably by aircooling, a bottom being used of which the thickness of the upper layerand of the lower layer are chosen depending on the heat conductiveproperties thereof and in which only 20 to 60 percent of the heatdischarge by the intermediary layer with a high heat conductioncoefficient is transferred to the lower layer.

The refractory upper layer has primarily as its function to protect theintermediary layer positioned below it. This is so because said lastlayer is made from a material which usually is much more expensive thanusual refractory materials.

As a suitable material for this thermally high conductive intermediarylayer it is according to the invention preferred to use graphite with aheat conduction coefficient of 60 to 100 kcal/m/h/C. By covering thegraphite layer by a less expensive layer from a material which isthermally more insulating, the temperature of the graphite layer isdecreased to below the melting temperature of the iron, so that it isavoided that the salamander is able to penetrate into the graphitelayer.

The lowermost layer, which again consists of a less conductive material,restricts the heat flow to and through the steel bottom slab. Theremainder of the heat is thereby discharged to the periphery of thegraphite layer, where the temperature is kept low by liquid cooling.

Due to the good heat conduction through the graphite layer it ispossible in applying the invention to obtain a temperature gradient fromthe top to the bottom which from place to place along the bottom isalmost the same everywhere, in the same way as would be possible if theheat flow through the graphite layer would mainly be discharged to thelower surface of the bottom. Due to the good and uniform heat dischargeit is thus only possible that a very shallow and particularly a veryflat salamander is formed.

An important advantage of the structure and the method according to theinvention moreover consists in that even for very large furnaces acooling by air of the lower side of the bottom is possible. Theconsiderable risks of water cooling in that zone are thus avoided.

It moreover appears that when decreasing the cooling, even with a totalfall-out of the air cooling, the temperature of the steel bottom slabrises only very slowly and reaches a temperature of 200 C only after avery long time, which opens the possibility to repair and switch on theair cooling again in time before the bottom temperature has risen toohigh.

It is remarked that a water cooling along the periphery of the furnacebottom gives considerably less risks than a water cooling of the lowersurface of the bottom. When falling out of the cooling along theperiphery it is always possible to cool this periphery in a simple wayby spraying water onto it by hand.

In U.S. Pat. No. 2,673,083 it has been proposed to build in a horizontalgraphite layer in the bottom of a furnace for the discharge of heat in asideways direction to a water cooling in the proximity of the peripheryof the bottom. However, in this case the graphite layer is enclosed in amassive refractory structure without cooling along the lower surface.This gives a heat discharge substantially entirely in a sidewaysdirection, with as a result a relatively deep profile of the isothermalsurfaces in the bottom. In such cases it appears necessary to cover thegraphite layer with a thicker upper layer in order to protect it, andthere will also be a deeper salamander. In general it may be said inthis respect that for the modern very large furnaces bottom structureswithout cooling along the lower surface become too heavy and tooexpensive to be attractive.

Particularly favourable results were obtained according to the inventionif 25 to 40 percent of the heat flowing through the intermediary layerwith high heat conduction coefficient is discharged to the lower layer,and if the periphery of the bottom is kept at a temperature of about 50C. Structurally it appears very well possible to realize such asituation, if in the lower bottom layer a material is used with a heatconduction coefficient of 2 to 5 kcal/m/h/C. Due to this low thermalconduction it is possible to apply only a thin layer for this lowerlayer. Good results can be obtained by applying amorphous carbon bricksin that area.

In the upper layer it is in principle possible to apply bricks ofcarbon, magnesite or chamotte (fire clay). Due to the very goodresistance against attack the application of a semi-graphite material ispreferred with a )t -value of 20 to 30 kcal/m/h/C. A particularlysuitable bottom was obtained with the structure having ascharacteristics that the three layers from top to bottom have -values ofabout 25, about and about 4 kcal/m/h/C respectively and that they havethicknesses of about 60, and 60 cm respectively.

Also very good results were according to the invention obtained if thebottom structure was moreover covered with a top layer with a thicknessof about 30 cm, the several layers from top to bottom consistingrespectively of magnesite (A 2 to 3), carbon (A about 5), graphite (Aabout 80) and carbon A 3 to 4), and having thicknesses of about 35,60,120 and 60 cm respectively.

The invention not only relates to the bottom structure and the method asdescribed above for cooling thereof, but in particular also to shaftfurnaces and in particular to blast furnaces for iron production, whichare provided with such novel bottoms. It has appeared that it ispossible to design such furnaces with lighter weight and that thecontrollability of the bottom temperature is more simple than in othercomparable furnaces.

As to the choice of the heat conduction coefficient A and the thicknessof the lower layer which together determine the thermal resistance ofthis layer, the following is remarked. If the thermal resistance ishigher (e.g., by a low A), the bottom slab will be cooler, but thesalamander will also be deeper. For a low thermal resistance of thelower layer more heat will be discharged through said layer, thetemperature of the bottom slab below the lower layer will increase, butthe salamander will be less deep and more plane.

By varying the structure of the lower layer such that of the total heatflow through the intermediary layer between 20 and 60 percent istransported through the lower layer, there will be obtainedcircumstances in hhich both the depth of the salamander and thetemperature of the bottom slab will be within acceptable limits. I

The invention will now be explained in more detail with reference to theenclosed drawing giving diagrammatically a possible embodiment of thenew bottom structure according to the invention.

In said figure reference numeral 1 indicates a steel jacket around arefractory bottom structure. This jacket merges into a steel bottom slab2, resting on a structure with supporting steel beams 3. The bottomitself is built up of three layers 4, 5 and 6. The upper layer 4 with athickness of 60 cm consists of semigraphite. Of this semi-graphite theheat conduction coefficient )t is about 20 kcal/m/hlC. Layer 5 has athickness of 120 cm and consists of graphite with a k of about 90kcal/m/h/C.

Layer 6 has thickness of 60 cm and consists of carbon bricks with a A ofabout 4 kcal/m/h/C. The said values relate to the values under operatingconditions and temperatures. The furnace diameter in the furnace hearthis about 13 in. By means of water spray cooling indicated by the spraypipes 7 jacket 1 is cooled to about 60 C. A fan not shown with a powerof 100 horse power serves to cool the steel bottom slab by air to keepits temperature below 100 C. The total quantity of heat 0,, dischargedthrough layer 5 is divided into two components. Heat flow Q through thebottom slab 2 is about 200,000 kcal/h and the quantity of heat Qdischarged through the jacket part of layer 5 is about 240,000 kcal/h.In the zone of the tap hole 8 the temperature within the furnace isabout 1,400 to 1,500 C. In the centre of the bottom the isotherm for1,100 C does not reach the upper side of layer 4, which is an indicationthat no salamander is able to form and that the bottom is not attacked.

It will be clear that the invention is not restricted to thisembodiment, which only serves to illustrate one possibility of realizingthe invention. In particular it is also possible to obtain good resultsby replacing the upper layer of semi-graphite by a carbonlayer of thesame thickness with a A value of 5 kcal/m/h/C, which is covered by alayer of magnesite of a thickness of 30 cm and a value of 2 to 3kcal/m/h/C.

We claim:

1. A bottom construction of a blast furnace or the like, whichcomprises, in combination:

a. a metal jacket around the periphery of the bottom of the furnace,

b. liquid cooling means around said metal jacket,

c. a metal bottom plate under the bottom of the furnace,

d. air cooling means beneath said bottom plate for cooling the same, and

e. three superimposed horizontal layers of refractory material supportedon said metal bottom plate, constituting an upper layer, an intermediatelayer, and a lower layer,

f. said intermediate layer having a heat conduction coefficient A, whichunder operating conditions, is higher than kcal/m/h/C, and

g. said heat conduction coefficient of said intermediate layer beingsubstantially higher than those of said upper and lower layers.

2. A bottom construction as claimed in claim 1, said intermediate layerhaving a A value of 60 to kcal/m/h/C.

3. A bottom construction as claimed in claim 2, said intermediate layerbeing a graphite layer.

4. A bottom construction as claimed in claim 2, said lower layer havinga A value of 2 to 5 kcal/m/h/C.

5. A bottom construction as claimed in claim 4, said lower layer being acarbon brick layer.

6. A bottom construction as claimed in claim 4, said upper layer havinga A value of 20 to 30 kcal/m/h/C.

7. A bottom construction as claimed in claim 6, said upper layer being asemi-graphite layer.

8. A bottom construction as claimed in claim 1, said upper, intermediateand lower layers having A values of about 2 5, 80 and 4 kcalIm/hPC,respectively, and thicknesses of about 60, and 60 centimeters,respectively.

9. A bottom construction as claimed in claim 8, said upper, intermediateand lower layers being semigraphite, graphite, and carbon-brick layers,respectively.

10. A bottom construction as claimed in claim 9 there being a fourthlayer interimposed on said upper layer, said fourth layer being amagnesite layer and having a thickness of about 35 centimeters.

11. A bottom construction as claimed in claim 1, the A values andthicknesses of said upper, intermediate and lower layers being such thatthe ratio of heat flows from the intermediate layer to said metal jacketand to said metal bottom plate, respectively, lies in the range of 80:20to 40:60. r

12. A bottom construction as claimed in claim 11, wherein said ratio ofheat flows lies in the range of 75:25 to 60:40.

13. A bottom construction as claimed in claim 12, wherein said ratio ofheat flows is about 240:200.

14. A bottom construction as claimed in claim 1, wherein duringoperation, the air cooling of the bottom plate maintains its temperaturebelow C.

15. A bottom construction as claimed in claim 14, wherein, duringoperation, the air cooling of the bottom plate maintains its temperaturebelow 50 C.

2. A bottom construction as claimed in claim 1, said intermediate layerhaving a lambda value of 60 to 100 kcal/m/h/*C.
 3. A bottom constructionas claimed in claim 2, said intermediate layer being a graphite layer.4. A bottom construction as claimed in claim 2, said lower layer havinga lambda value of 2 to 5 kcal/m/h/*C.
 5. A bottom construction asclaimed in claim 4, said lower layer being a carbon brick layer.
 6. Abottom construction as claimed in claim 4, said upper layer having alambda value of 20 to 30 kcal/m/h/*C.
 7. A bottom construction asclaimed in claim 6, said upper layer being a semi-graphite layer.
 8. Abottom construction as claimed in claim 1, said upper, intermediate andlower layers having lambda values of about 25, 80 and 4 kcal/m/h/*C,respectively, and thicknesses of about 60, 120 and 60 centimeters,respectively.
 9. A bottom construction as claimed in claim 8, saidupper, intermediate and lower layers being semi-graphite, graphite, andcarbon-brick layers, respectively.
 10. A bottom construction as claimedin claim 9 there being a fourth layer interimposed on said upper layer,said fourth layer being a magnesite layer and having a thickness ofabout 35 centimeters.
 11. A bottom construction as claimed in claim 1,the lambda values and thicknesses of said upper, intermediate and lOwerlayers being such that the ratio of heat flows from the intermediatelayer to said metal jacket and to said metal bottom plate, respectively,lies in the range of 80:20 to 40:60.
 12. A bottom construction asclaimed in claim 11, wherein said ratio of heat flows lies in the rangeof 75:25 to 60:40.
 13. A bottom construction as claimed in claim 12,wherein said ratio of heat flows is about 240:200.
 14. A bottomconstruction as claimed in claim 1, wherein during operation, the aircooling of the bottom plate maintains its temperature below 150* C. 15.A bottom construction as claimed in claim 14, wherein, during operation,the air cooling of the bottom plate maintains its temperature below 50*C.